The Efficiency of the bioinsecticide, Diple 2x (Bacillus thuringiensis) alone and its mixtures with two insecticides on cotton leafworm Spodoptera littoralis (Boisd) was investigated. Data indicated that Lufenuron was the highest effective insecticides against both the 2^nd and the 4^th instar larvae of S. littoralis followed by Methomyl and B.t , respectively .All tested mixtures decreased the toxicity according to Co-Toxicity factor ,the tested mixture (B.t + Lufenuron) gave the high level of antagonism effect followed by the mixture (B.t + Methomyle). The field efficiency of tested insecticides (when used singular) can be arranged according to the general mean of reduction percentage during two seasons in a descending order as follows: Lufenuron, Methomyle and B.t. The addition of B.t. to Lufenuron gave raising the general mean of reduction percentage during two seasons in contrast the other tested insecticide gave a reduction but less than when applied without added to Bt. The same trend of effects were obtained when applied the two tested insecticides at the half recommended rate alone or mixed with the same dose of Bt on S. littoralis but with less level of reduction in case of (Bt+Lufenuron) mixture.Also the three toxicants affected the Chitinase ,prptease and acetycholinesterase enzymes.